Highlight the "Rust" layer. That merges the rustlayer with the layer under it, in ouer case it should be the "Metal" layer.

The result should be something like this.

Now for the window. Turn on grid for some help. (Fastes way is Ctrl + ' or go to View/Show/Grid)
Now go to Edit/Preferences/Guides, Grid & Slices.

Set "Gridline every:" to 16 "Pixels"

Now select the Rectangular Marquee Tool (M), Set the feather to "1 Px".
Make a select box with a border of 1 gridbox.

Now chose Select/Modify/Contract and contract by 2 pixels. Delete the selection (Delete)

Highlight the "Background" layer and make a new layer, Name it "Window".
Fill it with a darkbluish color [#19191F].
Make another layer and Render it with clouds (Use primary color white secondary black "Filter/Render/Clouds" )

Change the Blending to overlay and merge the clouds layer with "Window" layer.

Voila the window is done. Should look something like this.

2. Alpha channel uses grayscale colors to controll transparency, the darker an area is on the textures alpha chanell the more transparensy it has. And the otherway around with white.

In the layers window switch to channels.

We need to duplicate one channels, Red, Green, Blue.
It's always good to use the whitet one. If can't find the whitest one try duplicating one at a time to check them. But for now we will go with "Red".

Drag the Red chanell on the New layer button.

That should create a whole new channel named "Red Copy".

Make sure that there's no selected areas and that "Red copy" (Alpha channel) is selected
Click on Image/Adjustments/""Brightness/Contrst"" and set the Brightness to about -45 and Contrast to about -70. Press OK.

Now go back to layers and CTRT + Click the "Metal" layer. (The Rusty metal border)
Go back to channels and click "Red Copy" Channel.
Press "Shift + Backspace". A Fill window should pop up, Use white as fill color. Press OK.

The selected area around the border should be white. The Red Channel should look like this

("$translucent" 1) This command gives hammer/game the command to use the Alpha channel we added in photoshop as a transparency layer.

("$nocull" 1) This command gives hammer/game the command to use the face on both sides of the face. NOTICE !!! To show a face both ways the brush has to use a func_
Best thing to use is a func_wall. But to show on the other side it allso has to be a few units thick or have a similar texture on the other side.